//        $("select[name=style_no]")[0].selectedIndex=(printer_info.style_no);
$("#style_no").selectedIndex=(printer_info.style_no);

jquery 获取select数组与name数组长度

可以用size() 或者options.length

$(“#name”)[0].options.length;或document.getelementbyid(“#name”).options.length;

$(“#name option”).size()

name:
$(“select[name=name]”).size();

option:
$(“#name option”).size();